Mode Ⅱ fracture parameters of concrete with different coarse aggregate volume fractions
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摘要: 对不同粗骨料体积分数下的混凝土Ⅱ型断裂性能进行了研究。根据最大泥浆厚度(Maximum paste thickness, MPT)理论,给出了断裂韧度KⅡ C与粗骨料体积分数Va之间的经验关系式。通过对含有四种粗骨料体积分数(19%、25%、31%、37%)的无切口试件开展半边加载断裂试验,测得相应的峰值荷载、断裂韧度、能量释放率等断裂参数,并分析了断裂韧带表面的裂纹分布规律。试验结果表明:随着粗骨料体积分数的增加,混凝土的Ⅱ型断裂韧度KⅡ C和临界能量释放率GⅡ C明显增加,名义断裂韧带处的裂纹轮廓线更长、更曲折;各配比试件的开裂模式基本一致,剪切裂纹主要集中在名义断裂韧带区域。同时,利用数字图像相关技术(Digital image correlation, DIC)对试件表面的损伤演化进行分析,结果表明,试件表面的应变局部化能够较好地表征断裂过程区(Fracture process zone, FPZ)的形态特征及演化过程。随着粗骨料体积分数的增加,FPZ的形态更不规则,分支更多。Abstract: This paper focuses on the mode Ⅱ fracture behaviors of concrete with different coarse aggregate volume fractions by laboratory experiments. Based on the maximum paste thickness (MPT) theory, the empirical relationship between the fracture toughness KⅡ C and the coarse aggregate volume fraction Va was proposed. The mode Ⅱ fracture parameters including peak load, fracture toughness and energy release rate were determined by the compression on half part of the non-notched specimen with different coarse aggregate volume fractions of 19%, 25%, 31% and 37%. The crack distribution on the surface of the fracture ligaments was analyzed. The results show that both mode Ⅱ fracture toughness KⅡ C and the critical energy release rate GⅡ C enhance with the increase of coarse aggregate volume fraction from 19% to 37% while the crack paths become more tortuous and longer with the increase of coarse aggregate volume fraction. The fracture patterns of all specimens are basically identical, even if the coarse aggregate volume fractions are different. It is found that the shear crack propagation is mainly around the middle ligaments. Additionally, the technique of digital image correlation (DIC) was employed during the tests to track the fracture evolution and characterize the strain localization regions as well as fracture process zone (FPZ). It is also observed by the DIC technique that there are more branches in FPZ and their shapes are more irregular as the coarse aggregate volume fraction increases.
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Key words:
- aggregate volume fraction /
- mode Ⅱ fracture /
- DIC /
- fracture toughness /
- damage evolution /
- fracture process zone (FPZ)
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表 1 水泥组成
Table 1. Composition of cement
Chemical composition/wt% SiO2 Fe2O3 Al2O3 CaO MgO Na2O K2O SO3 22.27 2.95 6.37 60.23 4.52 0.13 0.52 2.51 Mineral composition/wt% 3CaO·Al2O3 3CaO·SiO2 2CaO·SiO2 4CaO·Al2O3·Fe2O3 6.9 49.58 28.13 8.62 表 2 水泥力学性质
Table 2. Physical properties of cement
Loss on ignition/% Specific surface area /(m2·kg−1) fc/MPa ft/MPa Setting time/min 2.96 329 3d 28d 3d 28d Initial Final 23.5 50.3 5.6 8.8 196 258 Notes:fc is the compressive strength; ft is the tensile strength. 表 3 混凝土配合比
Table 3. Compositions of concretes
Group Specimen Cement/
(kg·m−3)Sand/
(kg·m−3)Coarse aggregate/
(kg·m−3)Limestone powder/
(kg·m−3)Water/
(kg·m−3)Superplasticizer/
(kg·m−3)Va/% C19 C19-01—C19-10 490 1 167 500 96 179.3 5 19 C25 C25-01—C25-10 490 1 000 667 96 179.3 5.5 25 C31 C31-01—C31-10 490 834 833 96 179.3 6.1 31 C37 C37-01—C37-10 490 667 1 000 96 179.3 7.4 37 Note:Va—Volume fraction of coarse aggregate. 表 4 含有不同骨料体积分数的混凝土断裂参数
Table 4. Fracture parameters of concretes with different volume fractions of aggregate measured from experimental tests
Va/% fc/MPa ft/MPa E/GPa KⅡ C/(MPa·m1/2) GⅡ C/(N·m−1) 19 44.79 3.80 33.23 2.21 146.98 25 51.96 3.59 32.30 2.91 262.17 31 50.08 4.41 34.01 3.17 295.47 37 58.36 4.85 35.26 3.41 329.78 Notes:E is the modulus of elasticity; KⅡ C is the mode Ⅱ fracture toughness; GⅡ C is the mode Ⅱ critical energy release rate. -
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